Control for heat-homing bomb



Feb. 25, 1958 A. W, FR|END CONTROL FOR HEAT-HOMING BOMB 2 Sheets-Sheet 1Filed Nov. 2l, .1946

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CONTROLFOR HEAT-HOMING BOMB 4 Filed Nov. 2l, 1946 2 Sheets-Sheet 2 EEEBlzffd mili IN VEN TOR.

BY M4.

Afrox/yay CoNTRoL Fon HEAT-HOMING BOMB Albert W, ldriend, Cambridge,Mass., assigner to the United States of America as represented by theSecr'etary of Wai' Appiicanon November 21, 1946, serial No. '711,456

4 Claims. (Cl.l B18-489) The invention described herein may bemanufactured and used by or for the Government for governmental purposeswithout payment to me of any royalty thereon.

This invention relates to the control system for a heathoming bomb ofthe type designed to be dropped at a high angle with the aid of abombsight in the same manner as a freely falling bomb, and capable ofsteering itself toward that part of the target area from which thegreatest amount of long wave length infrared radiation is being emitted.The steering of the bomb is accomplished by small elevator and ruddersurfaces which are located in the tail and serve to angularly displacethe axis of the bomb with respect to its velocity vector, the resultinglift produced by the body of the bomb being sufiicient to change thecourse of its fall. The bomb is stabilized as to roll by gyroscopicallycontrolled ailerons also located inthe tail.

The control system of the bomb comprises an infrared sensitive eyelocated inthe nose of the bomb, an electronic control circuit and aservo-mechanism for operating the control surfaces. The eye is capableof scanning an area toward which the bomb is moving of size commensuratewith the manueverability of the bomb and of producing a signal frominfrared radiations emanating from the area scanned. The electroniccontrol circuit analyzes the signal from the eye and causes theservomechanism to operate the control surfaces in such a way as to steerthe bomb toward the strongest source of infrared radiation in thescanned field.

It is the object of this invention therefore to provide a control systemof the above described type that is simple and reliable, and thatoccupies a minimum amount of space.

In the drawings:

Fig. l is a schematic diagram of the electronic control circuit;

Fig. 2 is -a simplified diagram of Fig. l for explaining the operationof the electronic control circuit; and

Fig. 3 is an analysis of the operation of the circuit of Fig. 2 throughone scanning cycle Vfor various target positions.

Referring to Fig. 1, the eye comprises a bolometer 1 located at theprimary focus of parabolic reflector 2 which is "mounted on shaft 3 insuch a way that its optical axis lmakes an angle of about 5 degrees withthe axis of the'shaft-and Vso 'that its primary focus falls on the axisof the shaft. The sensitive area of the bolometer is made circular andofsuch size as to subtend an angle at -Vthe optical center of the `reectorthat is twice the Aangle between the optical axis and the axis of theshaft, -in this case about degrees. With this arrangement the 'area on apiane perpendicular to the axis of the shaft, vor'` axisof rotation,from which radiations are caused to fall on the sensitive area of thebolometer is defined by a circle centered on the optical axis and havinga radius practically equal to the distance in theplane from the optical-axis to the axis of rotation. This circular scanning area is shownnited States Patent n FV' ICC at 4, the plane having been rotateddegrees from its true position for illustrative purposes. The shaft 3 isrotated at a constant speed of about 32 revolutions per second byconstant speed motor 5. This causes the scanning circle 4 to rotate andscan an area defined by the circle 6. When the scanning circle includesa sourceY of infrared radiation such, for example, as the ship target 7,the radiation from the target falls on the bolometer 1 and a signal isproduced. Also mounted on shaft 3 is a commutator 8, the details ofwhich are shown to the right of the eye." The function of the commutatoris to distinguish between signals received from the upper, lower, leftand right semicircles of the scanned area as will be explained later.

The bolometer 1 is an element whose electrical resistance changes withthe amount of infrared radiation falling on it. This element may be madeof a material having a high temperature coefiicientof resistance withthe resistive material coated with a black substance to convert the longwave length radiations into heat. The bolometer forms one arm of abridge circuit, the other three arms of which vare composed of balancingresistor 9 and the two halves of the primary winding of transformer 10.The resistor 9 should have a value as nearly equal as possible to theresistance of bolometer 1 at its normal operating tempera-- ture in theabsence of a signal. Operating current for the bridge is obtainedthrough grounded leadll which is con-V nected to point 12 of the bridge,and through lead 13 which is connected between opposite point 14 of thebridge and the -6 v. terminal through relay 15 when this relay isenergized by application of voltage to the +24 v. terminal. The resistor16 serves to limit the bridge cur-V rent to the proper operating value.

When the scanning area 4 includes the target, infrared radiationtherefrom falls on the bolometer 1 and causes its resistance toincrease. This increase is represented by the o-m portion of the waveshown in Fig. 1 at (a). During the time when the scanning area does notinclude the target, the bolometer cools and its resistancev decreases asrepresented by the m-21r portion of the wave. Thus a saw tooth wave ofresistance change is produced at the scanning frequency of about 32cycles per second. This change in resistance causes an unbalance betweenthe currents in the two halves of the primary winding and the resultantiiux produced by the unbalance induces a voltage in the secondarywinding. Due to the filtering action ofV the transformer and itsinability to pass the direct component of a wave, an alternating voltageis produced inthe secondary which approaches a sine wave in shape asshown at (b). The frequency of this voltage is likewisev 32 cycles persecond.

The secondary voltage is applied between the grid and triode V3. Thenecessary grid bias for V2 is supplied by" the voltage drop acrossresistor 19 which is connected in series with resistor 20 between the -6v.'terminal and ground.

The dual triode V3 acts as an amplifier and also as a phase inverter forcoupling the unbalanced output circuit' of tube V2 to the input circuitof V4, which is balanced with respect to ground. Considering the upper'section of V3, the signal from the output circuit of V2 is applied bei"tween the control grid 21 and ground. The cathode's of the two sectionsare connected together and to'grolundi: through resistor 22. The grid 23of Vthe'lower sectionisjconnected through resistor '24, 'th'e'lower end'of 'which"$' at ground potential asfar as the signal is concernedbecause of the lter condenser 25. Assume that the signal causes thepotential of grid 21 to increase in a positive direction, then thecurrent flowing in resistor, 22 due to the upper section increases andthe cathodes of the two sections become more positive with respect toground or, in other words, grid 23 becomes more negative with respect toits cathode. The signal potentials on grids 21 and 23 are therefore 180degrees out of phase and likewise the anode currents in the two sectionsof V3 are 180 degrees out of phase. Since the anode currents ot bothsections flow through resistor 22, the voltage drop across thisresistor, which constitutes the signal applied to grid 23, is thevoltage drop produced by the difference in these two currents. Thecircuit therefore must adjust itself to a slightly unbalanced conditionin which the anode current of the lower section is less than that of theupper section by an amount just sufficient to provide the proper signalvoltage ou grid 23. The degree of unbalance is an inverse function ofthe amplification of the lower section of V3.

' The output signal of V3 is applied to the grids of tube V1 throughcoupling condensers 26 and 27. The tube V4 is part of a conventionalresistance coupled push-pull stage having a feedba-ck resistor 28 commonto the anode and grid circuits of both sections of the tube. If thestage is perfectly balanced, the two anode currents tiowing throughresistor 28 are of equal amplitudes and 180 degrees out of phase. Theresultant current is therefore zero and no signal is developed acrossresistor 28. However, if the currents in the two sections tend to becomeunequal, a signal is developed across resistor 28 proportional to thediference in the two currents. This signal is fed back to the two gridsin such phase as to increase the signal on the grid'of the sectionhaving the lesser current and to decrease the signal on the grid havingthe greater current. The effect of resistor 28 therefore is to maintaina balance between the anode signal currents of the two sections of tubeV4.

A positive potential obtained from the drop across resistor 29 isapplied to the grids of tubes V3 and V4 by means of conductor 31.Resistor 29 is connected in series with resistor 30 between a source ofpositive direct potential and ground. The potential across resistor 29is adjusted to such a value that the difference between this potenti-aland that produced across resistors 22 and 28 by the steady directcomponent of the anode currents of tubes V3 and V4 gives the properbiasing potential for these tubes.

In order to convert the sine wave output of transformer to substantiallya square wave, resistors 32, 33, 34 and 35 having values of from one totwo megohms are inserted in series with the grids of tubes V2, V3 IandV4. Sufficient amplification is provided so that the signals applied tothe input circuits of these tubes are of considerably greater amplitudethan that required to drive the grids positive. Since the grids can goonly slightly positive due to the drop in resistors 32 through 35 whengrid current begins to ow, the result is a squaring of the positive.half cycle of the signal. Due to the ph-ase reversals produced by thetubes, both half cycles of the signal are` subjected to this squaringaction. Any inequality in the amplitudes of the two half cycles of thesignal appearing across resistors 36 and 37 is removed by condensers 38and 39 through their inability to pass the direct current component ofthe signal, so that there appears across resistors 40 and 41 asymmetrical alternating voltage E substantially square in forni as shownin Fig. 2.

The commutator 8 comprises four sets of contacts 42-43, 44-45, 46--47and 48-49,V and a cam 50 mounted on shaft 3. Cam followers 51, 52, 53and 54 are arranged to open and close the contacts and to contact thecam at points 90 degrees apart. The cam is cut so that each set ofcontacts .is closed for about 175 degrees of the cams rotation. Contacts42 and 44 are connected together as are also contacts 46 and 48, and thevoltage E is applied between these two pairs of common contacts.Contacts 45 and 49 are connected together and through resistor 55 to oneside of condenser C1, the other side of which is connected to ground.Likewise contacts 43 and 47 are connected together and through resistor56 to one side of condenser C2, the other side of which is connected toground. When either contacts 44-45 or 48-49 are closed, the condenser C1is subjected to a potential that acts to charge or discharge thecondenser depending upon the charge already in the condenser when thecontacts close and the polarity of points B or A during the time thecontacts are closed. Similarly a potential is applied to condenser C2through resistor 56 when contacts 42-43 or 46-47 are closed, the effecton the condenser being determined by the previous condition of chargeand the polarity of point B or A during the time the contacts areclosed. Therefore, when the cam 50 rotates, a series of voltage pulsesis applied to condensers C1 and C2. These pulses will be all positive,all negative, or mixed positive and negative depending upon the phaserelationship between the voltage wave E and some reference point on thecam 50 or the scanning cycle.

The condenser C1 is connected between the grid and cathode of the uppersection of V6 and the condenser C2 is connected between the grid andcathode of the lower section of this tube. Hence, the potentials acrossthese condensers determine the potentials between the grids and cathodesof the two sections of V6. Resistors 57 and 58 have equal values landare connected between the -6 v. terminal and ground. The resulting 3volt drop across resistor 57 is applied through resistors 40 and 41, thecontacts of commutator S and resistors 55 and 56 tothe condensers C1 andC2. Therefore, in the absence of a signal, these condensers are chargedto a potential of 3 volts with the ungrounded sides negative, whichpotential supplies the operating bias for the two sections of tube V6.The cathode of the upper diode section of V5 is connected to theungrounded side of condenser C1 and the cathode of Vthe lower diodesection to the ungrounded side of condenser C2. The anodes of the twodiodes are connected together and to ground through the -6 v. source ofpotential. The anodes of the two diodes are therefore biased 6 voltsnegative with respect to their cathodes. With this arrangement, thecondensers C1 and C2 may charge to a potential of 6 volts with theungrounded side negative but any further charging will be prevented bythe shunting effect of the diodes which become conductive at this point;4also the condensers C1 and C2 may discharge to zero potential but anyrecharging with reversed polarity is prevented by the shunting effect ofthe grid-cathode paths of the two sections of V6 which becomesconductive at this point. Hence potential variations across condensersC1 and C2 are limited to a maximum of 3 volts in either direction fromthe 3 volt potential normally existing thereacross in the absence of asignal, and as a result the potential variations of the grids of tube V6are limited to a maximum of 3 volts either side of the bias potential of-3 volts.

Considering again the series of Voltage pulses applied to condensers C1and C2, if all the pulses are positive or if the positive pulsespredominate in number, the condensers discharge and the grid potentialsare raised; if all pulses are negative or if negative pulses predominatein number, the condenser charges are increased and the grid potentialsare lowered; if there are equal numbers of positive and negative pulses,Ytheir net effect on the condenser charges is zero and the condenserseither remain at or return to their normal no-signal charge, dependingupon whether the condensers were previously at their normal charge orhad been charged or discharged to a voltage greater or less than 3lvolts. The values of condensers C1 and C2 and resistors 55 Iand 56 aresuch that the time constants of the two condenser circuits aresufficiently long to require a signal to remain for about six cycles ofthe scanning system in order to appreciably change the charge on thecondensers.

The coils of relays 59 and 60 are connected in the anode circuits of theupper and lower sections respectively of V6. These relays are adjustedso as to operate when the grid potentials reach a value slightly above 3volts. For grid voltages below this value, the anode currents areinsuicient to operate the relays. The contacts of these relays are incircuit with the servomotors operating the control surfaces of the bomb.Thus when relay S9 is operated the D contact is closed and a downcorrection is made in the bombs direction of travel; likewise, whenrelay 60 is operated, the R contact is closed and a right correction isapplied. In the deenergized condition, the U contact of relay 59 and theL contact of relay 60 are `closed so that in the absence of a signal thebomb is made to follow an up and to the left course. Thus the bombfollows a sinuous path toward the target.

The operation of the commutator may be more clearly understood byreference to Fig. 2. In the simplified diagram of this gure thesemicircular conductive strips 61, 62, 63 and 64 each extend for about175 degrees and with contacts 65 and 66 which rotate together, form anarrangement that is the electrical equivalent of commutator 8 in Fig. 1.The scanning area 4 and arrow 67 also rotate with contacts 65 and 66.The arrow 67 represents the angular position of the point at which thescanning area begins to include the target, which is the point at whichvoltage wave E is initiated. As previously shown the period of voltagewave E is the same as that of a complete scanning cycle. Theintersection of the Up-Down and the Right-Left axes represents the pointtoward which the bomb is travelling. Hence if the target is above theLeft-Right axis, an up correction is needed and if to the right of theUp-Down axis, a right correction is needed, etc.

Fig. 3 gives a tabulation of the polarities of the voltage pulsesapplied to condensers C1 and C2 for eight points on the scanning cycleand for Various angles of lag between the arrow 67 and the voltage waveE. The angle of lag is the angle through which arrow 67 rotates from thezero position before voltage wave E is initiated and is determined bythe position of the target. The first column of the table shows thepulse polarities for zero phase angle which is the condition in whichthe voltage wave E is initiated when the arrow 67 is in the zeroposition, and is the condition shown in Fig. 2. Therefore for 180degrees of the scanning cycle the point A, Fig. 2, will be positive andthe point B negative. Since strip 61 is connected to point B and sincecontact 65 is on this strip for approximately 180 degrees, the potentialapplied to C1 from 0 to 180 degrees is negative as shown under C1. Sincecontact 63 is also connected to point B, the potential applied to C2from 0 to 90 degrees is also negative as shown under C2 However, from 90to 180 degrees, contact 66 is on strip 64 which is connected to point Aand therefore the potential applied to C2 during this interval ispositive. From 180 to 360 degrees, the point A is negative and the pointB positive due to the reversal in polarity of E at 180 degrees.Therefore the voltage applied to C1 through contact 65 during the180-360 degree interval is also negative, whereas the voltage applied toC2 through Contact 66 is negative from 180 to 270 and positive from 270to 360 since this contact changes from strip 64 to strip 63 at 270degrees. Therefore it is seen that for this phase angle the charge of C1is increased and the grid of the upper section of V5 becomes morenegative so that relay 59 is not operated; and since the voltage appliedto C2 alternates equally between positive and negative polarity withneither polarity persisting long Yenough to appreciably change thecharge of this condenser, the grid voltage of the lower section remainsat -3 volts and the relay V60 is likewise not operated. The correctionproduced for this target position is therefore up and left A similaranalysis of the operation of the circuit for lag angles `from .'45 to315 degrees is given'in'the remaining columns of the table in Fig. 3,with the' correction' produced in each case given at the bottom. It willbe noted that whenever the target is on the Up-Down axis, a leftcorrection is given and whenever it is on the Right-Left axis, an upcorrection is given. If the target is at the intersection of the twoaxes, an up and left correctin is given. This is due to the previouslymentioned fact that in the deenergized condition the U and L contacts ofrelays 59 and 60 are closed and is the reason for the aforementionedsinuous path taken by the bomb in travelling toward the target.

What I claim is:

1. A control system for a target seeking bomb comprising a circularscanning device and a thermal infrared sensitive device the resistanceof which changes with temperature changes due to changes in the amountof infrared radiation falling thereon, said scanning device and saidinfrared sensitive device cooperating to produce a cyclic variation inthe resistance of the infrared sensitive device at the frequency of thescanning cycle whenever a source of infrared radiation appears in thescanned field, the phase relation between said cyclic resistancevariation and said scanning cycle being determined by the position ofthe source of infrared radiation in the scanned field, means forchanging said cyclic resistance variation into substantially a sine Waveof voltage having the same frequency as the resistance variation, saidchanging means having an output circuit that is unbalanced with respectto ground, means for amplifying said voltage wave and converting saidunbalanced output circuit into a circuit that is balanced with respectto ground, said amplifying and converting means also containing meansfor clipping the sine wave of voltage so that a substantially square ofvoltage is produced in said balanced circuit, commutating meanscomprising a cam and four sets of contacts, cam follower meanscontacting said cam at points ninety degrees apart and arranged to openand close said contacts, said cam being shaped to close each set ofcontacts for slightly less than one hundred and eighty degrees of thecams rotation, two condensers with one side of each connected to ground,means connecting the electrical center of said balanced circuit toground through a source of constant direct voltage, means connecting oneside of said balanced circuit through two of said sets of contactsoperated by adjacent cam followers to the ungrounded side of each ofsaid condensers, means connecting the other side of said balancedcircuit through the remaining two of said sets of contacts to theungrounded side of each of said condensers, a plurality of controlcircuits associated with the steering mechanism of the bomb, relay meansfor opening and closing said control circuits, and means utilizing thevoltage across said condensers to control the operation of said relaymeans.

2. Apparatus as claimed in claim 1 in which each of said condensers hasa resistor connected in series therewith of such value as to require anychange in signal to persist for several scanning cycles in order toappreciably change the voltage across said condensers.

3. Apparatus as claimed in claim 1 in which said utilizing meanscomprises two electron tubes each having the coil of one of said relaymeans in its anode circuit and each having one of said condensersconnected between its grid and cathode, and in which each of saidcondensers is shunted by a diode biased by a voltage equal to twice thevoltage of said source of contant direct voltage whereby voltagevariations across said condensers References Cited in the le of thispatent i UNITED STATES PATENTS Rost et al July 1.5, 1947

